[ValueTracking] Enabling ValueTracking patch by default (recommit). Part 1.

[ValueTracking] Enabling ValueTracking patch by default (recommit). Part 1.

The original patch was an improvement to IR ValueTracking on non-negative
integers. It has been checked in to trunk (D18777, r284022). But was disabled by
default due to performance regressions.
Perf impact has improved. The patch would be enabled by default.

Reviewers: reames, hfinkel

Differential Revision: https://reviews.llvm.org/D34101

Patch by: Olga Chupina <olga.chupina@intel.com>

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@310582 91177308-0d34-0410-b5e6-96231b3b80d8